added docs comments

lib/src/models/documents/attribute.dart

@@ -342,23 +342,23 @@ class HeaderAttribute extends Attribute<int?> {
       : super('header', AttributeScope.block, level);
 }
 
+/// This attribute represents the space between text lines. The line height can be
+/// adjusted using predefined constants or custom values
+///
+/// The attribute at the json looks like: "attributes":{"line-height": 1.5 }
 class LineHeightAttribute extends Attribute<double?> {
   const LineHeightAttribute({double? lineHeight})
       : super('line-height', AttributeScope.block, lineHeight);
 
-  /// "attributes":{"line-height": 1.0 }
   static const Attribute<double?> lineHeightNormal =
       LineHeightAttribute(lineHeight: 1);
 
-  /// "attributes":{"line-height": 1.15 }
   static const Attribute<double?> lineHeightTight =
       LineHeightAttribute(lineHeight: 1.15);
 
-  /// "attributes":{"line-height": 1.5 }
   static const Attribute<double?> lineHeightOneAndHalf =
       LineHeightAttribute(lineHeight: 1.5);
 
-  /// "attributes":{"line-height": 2.0 }
   static const Attribute<double?> lineHeightDouble =
       LineHeightAttribute(lineHeight: 2);
 }

lib/src/widgets/quill/text_line.dart

@@ -304,6 +304,8 @@ class _TextLineState extends State<TextLine> {
           defaultStyles.lineHeightDouble!.style,
     };
 
+    // If the lineHeight attribute isn't null, then get just the height param instead whole TextStyle
+    // to avoid modify the current style of the text line
     textStyle =
         textStyle.merge(textStyle.copyWith(height: x[lineHeight]?.height));